This application is for a Physician Scientist Award for an MD who will have had two years of postgraduate house staff training. In Phase I (two years), 25-30% of the applicant's time will be devoted to formal course work in basic molecular biology. The remaining time in these years and Phase II will be devoted to pursuing the research project below. Eucaryotic cells contain a number of small ribonucleoproteins (RNPs) which consist of one or more proteins closely associated with a small RNA molecule. Autoantibodies from patients with rheumatic disease have been used to purify small RNPs and define their functions in mammalian gene expression. Here, small RNPs involved in the nucleolar biogenesis of ribosomes will be investigated. Three of the four rRNAs found within mature ribosomes are synthesized from cleavage of a single 45S rRNA precursor. It has been demonstrated that the 216 nucleotide U3 RNA contained within the RNP designated as U3 RNP is capable of forming an 8 base-pair perfect duplex with the 5' end of the internal transcribed spacer (ITS)-II separating 5.8S rRNA from 28S rRNA in the pre-rRNA molecule. Because of this complementarity it has been proposed, but not yet proven, that the U3 RNP is involved in processing pre-rRNAs. The fourth rRNA designated 5S rRNA is transcribed from chromosomal DNA within the nucleoplasm and then transported to the nucleolus. Mature 5S rRNA is found transiently as part of an RNP called 5S RNP, the function of which is unknown. Possible role for the 5S RNP include control of transcription of the 5S rRNA or the other rRNAs, control of transcription of ribosomal protein mRNA, and transport or processing of 5S rRNA. To define the structure and function of the mammalian U3 RNP and 5S RNP, two specific patient autoantibodies, anti-U3 RNP and anti-5S RNP, will be used to characterize their total and antigenic protein constituents and to identify the protein binding sites on the RNAs. The function of the particles will be investigated by blocking various in vitro reactions with antibodies, then attempting to restore activity with intact particles.